The health burden from beta-hemoglobinopathies and thalassemias is enormous. Increased fetal hemoglobin[unreadable] (HbF) ameliorates the severity of these disorders. While much progress has been made in an understanding[unreadable] of the "hemoglobin switch" from gamma- to beta-globin, specific intracellular regulators of this critical developmental[unreadable] event are unknown and the switch cannot be reliably manipulated in patients. This research is focused on[unreadable] new approaches to the hemoglobin switch that rely on genetic, rather than strictly biochemical or molecular,[unreadable] strategies. Progress in several areas suggests that the time is propitious for new initiatives. Several[unreadable] independent, but complementary, approaches will be taken. First, integrative genomic analysis will be[unreadable] applied to identify the specific locus at chromosome position Xp22 that has previously been linked to F-cell[unreadable] production by other investigators. Preliminary in silico analyses suggest a limited number of candidate genes[unreadable] within this interval. Candidates will be validated or excluded by association studies using high-density SNPs,[unreadable] sequencing of highly likely candidates, and functional studies in mouse erythroid cells harboring the human[unreadable] beta-globin locus. The aim is to identify the first trans-regulator of the hemoglobin switch. Second, high-level[unreadable] HbF expression is a hallmark of the rare pediatric malignancy juvenile myeloid leukemia, a disorder that[unreadable] arises sporadically or in the setting of Noonan's syndrome and neurofibromatosis type I. A common feature[unreadable] is mutation of PTPN11 or neurofibromin with consequent activation of the Ras pathway. Based on these[unreadable] clinical observations, the hypothesis that increased Ras activity stimulates gamma-globin production will be[unreadable] pursued through the study of engineered mice that have been made available for these studies. If the Ras[unreadable] pathway is validated as a modulator of HbF expression, this finding would open the way to consideration of[unreadable] new therapeutic approaches to influencing the hemoglobin switch in patients. In parallel, the potential role of[unreadable] the newly identified factor zfp148 in hemoglobin switching will be pursued in collaboration with Dr. Cantor[unreadable] (Project 4). Finally, unbiased genetic screens will be initiated to identify genes whose expression either[unreadable] promotes or inhibits gamma-globin expression. An appropriate "reporter" mouse erythroid cell line will be used in[unreadable] both genome-wide siRNA and retroviral insertional mutagenesis screens. Through these multidisciplinary[unreadable] approaches unrecognized regulators of the hemoglobin switch will be discovered.